The Science of Earthquakes in Chile and Japan
Edit 3/12/11 — For information on the Sendai, Japan earthquake of Friday, March 11, 2011 and a link to the real time world earthquake map, go to this new post.
A massive magnitude 8.8 earthquake hit Chile at 3:34 am local time this morning (February 27, 2010). Strong aftershocks of up to magnitude 6.9 have rocked the region and will continue throughout the next few days to weeks. Click on the map to go to the current version of the USGS’s real-time world earthquake tracking map.
The Chilean earthquake follows a magnitude 7.0 earthquake that shook Japan at 5:31 am local time yesterday (February 26, 2010). That quake was originally reported as a 6.9, but later reports revised this to 7.0. This quake was centered in the Philippine Sea, just southeast of the city of Okinawa in the Ryukyu islands of Japan.
Details of the Ryuku Islands Earthquake The February 26 th earthquake in Japan was centered in the Philippine Sea, 50 miles southeast of the city of Okinawa, Japan. This earthquake caused modest to strong shaking to the islands, resulting in only minor damage. Thankfully as of this morning only 2 injuries and no deaths have been reported. The United States Geological Survey (USGS) says that this earthquake likely occurred in within the Philippine Sea tectonic plate, near the boundary of the Philippine Sea plate and the Eurasian plate, although the quake could have occurred at the plate boundary, its difficult to distinguish between the two possibilities. This plate boundary is a subduction zone. A subduction zone is where one tectonic plate slides under another. In this case, the Philippine Sea plate is moving northwest relative to the larger Eurasian plate and sliding under the plate at the Ryukyu Trench. The two plates are moving at a rate of 60 millimeters each year.
Details of the Chile Earthquake Unfortunately, the Chilean earthquake was far more powerful and destructive than the Japanese earthquake. The magnitude 8.8 earthquake is the largest earthquake yet this year. Early reports indicate there is massive damage, with collapsed buildings, electrical outages and damaged roads. The death toll stands at 82 people and rising quickly.
The Chilean quake was also centered offshore, about 200 miles southwest of the capital, Santiago. According to the USGS, the earthquake occurred at the boundary of the Nazca and South American tectonic plates. This plate boundary is also an active subduction zone. The Nazca and South American plates are moving together at a rate of 80 millimeters each year, with the Nazca plate moving east and sliding under the South American plate. These are different plates and a different boundary area from the plates that were involved in the Haiti earthquake of January 2010. That earthquake occurred along the boundary of the North American and Caribbean plates. For more on the science behind the Haiti earthquake, click here.
Why do earthquakes happen? (from my earthquake in Haiti post) The Earth’s crust is not one solid mass. It’s a series of large (like, larger than continent size large) slabs called tectonic plates that float on the more molten middle part of the earth, called the mantle.
These plates move around on the upper mantle and interact with each other in a number of different ways. The areas where this interaction occurs are called plate boundaries or boundary environments. One of the more dramatic examples of this interaction is the formation of the Himalayas on the border between India and the Tibetan plateau. The Indo-Australian plate is pushing northward into the Eurasian plate, causing both plates to buckle upward, forming the mountain range. Geologists call this process orogeny, from the Greek for “mountain building.” What’s really cool is that this process is still going on. The Himalayas grow about a centimeter (just under half an inch) every year
The earthquake in Chile happened in a process called thrust faulting. This is where the Nazca and South American plates moved suddenly, with the Nazca plate moving down and landward under the South American plate. The earthquake in Japan was probably caused by a similar mechanism, from the Philippine Sea plate slipping under the Eurasian plate, although reports from the USGS indicate that this earthquake could have been centered within the Philippine Sea plate and not on the plate boundary.
Tsunami advisories and warnings issued The Ryukyu Islands earthquake triggered an initial tsunami advisory for the islands themselves. This advisory was canceled and only minor waves struck the island. The Chilean earthquake triggered tsunami advisories and warnings as far away as Alaska and New Zealand. Early reports indicate a tsunami hit the Robinson Caruso islands, just east of Chile. Thankfully no deaths have been reported from tsunamis yet, but alerts will likely remain in place until tomorrow (February 28, 2010).
How do the Chile and Ryukyu Islands quakes relate to other recent quakes? The February 2010 Chile earthquake was a magnitude 8.8, and the February 2010 Okinawa quake measured 7.0. The January 2010 Haiti earthquake was also measured at a magnitude 7.0. A Richter scale is not the name of the devise used to measure the shaking (that’s a seismograph). The Richter scale takes seismograph information and turns it into a number representing the magnitude of the earthquake. For every whole number increase on the scale, the magnitude increases by a factor of ten. This means an earthquake of magnitude 7.0 is ten times more powerful than one of magnitude 6.0, making an earthquake of magnitude 8.8 a significant earthquake.
History of earthquakes in both regions Chile and Japan both have a history of powerful earthquakes. In fact, the most powerful earthquake ever recorded (magnitude 9.5) occurred in Chile in 1960, and since 1973 there have been 13 earthquakes of magnitude 7.0 or greater in Chile. A magnitude 7.2 earthquake in 1995 caused massive damage and killed 6,400 in the city of Kobe, Japan.